The present invention relates to blowout preventers and, more particularly, relates to a rotating blowout preventer with spherical packing elements for use in hydrocarbon recovery operation. The blowout preventer of this invention is able to reliably withstand high pressure while maintaining sealed engagement with a tubular rotating at relatively high speeds, and also may be used to seal with a non-rotating tubular.
Rotary blowout preventers for oil well drilling operations have existed for decades. U.S. Pat. No. 3,492,007 discloses a blowout preventer (BOP) for sealing well pressure about a rotating kelly or other production tool. U.S. Pat. No. 3,561,723 discloses a blowout preventer designed to prevent fluid from escaping from the well while the pipe string is either rotating or stationary. U.S. Pat. No. 4,098,341 discloses a rotating blowout preventer which is supplied with pressurized hydraulic fluid to lubricate and cool bearings within the BOP.
U.S. Pat. No. 4,378,849 discloses a blowout preventer with a mechanically operated relief valve to release high pressure surges in the annulus between the casing and the drill pipe sealed by the BOP packing. U.S. Pat. No. 4,383,577 discloses a rotating drilling head assembly which provides for the continuous forced circulation of oil to lubricate and cool thrust bearings within the assembly. A technique for fluidly connecting an outlet port of a BOP and an inlet of a choke manifold is disclosed in U.S. Pat. No. 4,618,314. The fluid may be injected into the blowout preventer for pressure testing and for charging the equipment with a desired fluid.
U.S. Pat. No. 5,178,215 discloses a rotary blowout preventer with a replaceable sleeve having a plurality of grippers therein. The blowout preventer disclosed in the ""215 patent utilizes an inner packer which is responsive to hydraulic pressure to act against a sleeve which engages the drill pipe. The hydraulic fluid pressure which causes radial movement of the inner packer is sealed within the body of the BOP by seal assemblies which must withstand a pressure differential in excess of the difference between the well pressure and atmospheric pressure.
Improvements in rotating blowout preventers are required so that the blowout preventer may reliably withstand higher pressures, such as the high pressure commonly associated with underbalanced drilling. Underbalanced drilling occurs when the hydrostatic head of the drilling fluid is potentially lower than that of the formation being drilled. Underbalanced drilling frequently facilitates increased hydrocarbon production due to reduced formation damage, and results in both reduced loss of drilling fluids and reduced risk of differential sticking.
The disadvantages of the prior art are overcome by the present invention, and an improved blowout preventer and method of operating a blowout preventer are hereinafter disclosed. The blowout preventer is able to withstand high pressure while maintaining sealed engagement with a tubular rotating at relatively high speeds, and may also be used to seal with a non-rotating tubular.
The rotating blowout preventer of the present invention may be compatible with either kelly or top drive drilling systems. The spherical sealing assembly is capable of being used to strip tubulars and oilfield tubular connections, and will reliably seal with different diameter tubulars. The seal assembly may also maintain high pressure integrity when the tubular passing through the assembly is not rotating. Further, the spherical sealing assembly may seal off a well bore when no tubular is passing through the sealing assembly.
The rotating blowout preventer (RBOP) of the present invention is capable of reliable operation when the pressure differential between the well bore and atmosphere is in excess of 2000 psi and while the tubular is rotating at speeds of up to 200 rpm. The unit may also function as a non-rotating annular BOP with working pressure of up to 5000 psi. The assembly includes the ability for a complete shutoff of the empty bore at up to 2500 psi.
The spherical sealing element is actuated in response to axial movement of a fluid pressure piston. In order to minimize the diameter of the rotating seals, no rotating seals are provided on the outside diameter of the piston when applied fluid pressure causes sealing engagement of the spherical sealing elements. The piston closing force is generated by fluid pressure acting on the relatively large cross-sectional rod area of the piston between the lower seal and an upper adapter ting seal. The comparatively small cross-sectional flange area of the piston between the upper and lower adapter ring seals is used to open the RBOP. The piston and the adapter ring rotate together, and accordingly seals between these components are non-rotating.
The RBOP assembly includes a lower rotary seal between the stationary lower housing and the inner sleeve of the rotating piston. Closing pressure from the hydraulic supply to the RBOP is maintained at a selected value above the well bore pressure, so that this lower rotary seal is only exposed to a pressure differential of this selected value, e.g., from 200 psi to 500 psi. The upper rotary seal acts between the stationary upper housing and the rotating inner housing. A significant pressure drop is achieved across a restrictive flow bushing upstream of the upper rotary seal. The restrictive bushing floats radially with the rotating inner housing to accommodate eccentricity without generating excessive friction. The piston effect of the restrictive bushing prevents fluid flow between the bushing and the stationary upper housing and then above the bushing to the fluid outlet port. The hydraulic fluid thus passes between the outside diameter of the rotating inner housing and the inside diameter of the restrictive bushing to maintain a substantially uniform gap between the bushing and the inner housing. This substantially uniform gap may be maintained by a restrictive bushing radial bearing. The pressure of the hydraulic fluid drops significantly and at a substantially constant amount across the bushing, so that pressure acting on the upper rotary seal is continually only slightly greater than atmospheric pressure. Accordingly, the elastomeric upper rotary seal reliably isolates the low pressure hydraulic fluid from the environment.
The upper rotary seal and the lower rotary seal preferably have a diameter as small as practical, and also preferably have substantially the same diameter to balance the forces acting on the rotary components of the assembly. Pressurized fluid to the RBOP is provided in a closed loop system since fluid continuously flows past the restrictive flow bushing to maintain the desired low pressure drop across the upper rotary seal. The flow path of hydraulic fluid through the RBOP when the sealing elements engage the rotating tubular is past the lower rotary seal, then radially outward of the piston and the sealing assembly, past an inner housing thrust bearing, then past the restrictive flow bushing. The thrust bearing is spaced radially outward of and axially within the same plane as the restrictive flow bushing to reduce the axial height of the RBOP. The restrictive flow bushing preferably fits between cylindrical surfaces on the stationary upper housing and the rotary inner housing which each have an axis concentric with the central axis of the RBOP.
An opening chamber is formed between the upper and lower adapter ring seals and between the adapter ring and the piston. Although no outer rotating elastomeric seals are provided on the piston, the opening pressure to the RBOP is substantially restricted from passing beneath the piston by a metal-to-metal restriction between the adapter ring and an adapter ring bearing race. Since the sealing assembly is not rotating when the RBOP is opened, this metal-to-metal restriction need only be a static restriction.
It is an object of the present invention to provide an improved rotary blowout preventer which utilizes a spherical sealing assembly. A further object of the present invention to reduce to pressure applied to the upper rotary seal of an RBOP by providing a flow restrictive member upstream of the upper rotary seal, and continuously circulating fluid past the flow restrictive member.
It is a feature of the present invention that hydraulic fluid supplied to the RBOP for actuating the sealing assembly is first directed past the lower seal assembly, then in a path radially outward of both the actuating piston and the sealing assembly, then past an inner housing thrust bearing, and finally past a restrictive member which reduces the differential pressure applied to the upper seal assembly. It is a further feature of the present invention that the thrust member is radially outward of and in substantially the same horizontal plane as the flow restrictive member to reduce the height of the RBOP. A further feature of the invention is that the flow restrictive member resides between the cylindrical surfaces each having an axis substantially concentric with a central axis of the RBOP. Still another feature of the invention is the ability to reliably open the RBOP in response to fluid pressure applied to the RBOP and without providing a dynamic elastomeric seal on the outer diameter of the piston.
It is an advantage of the present invention that the rotating blowout preventer may also reliably seal under high pressure against a non-rotating tubular passing through the RBOP. The sealing assembly of the RBOP is able to reliably seal against different sized tubular members or against a non-tubular member passing through the RBOP. The sealing assembly further has the ability for a complete shutoff of the well with no tubular passing through the RBOP. The RBOP assembly is capable of being used to strip various tubulars and oilfield tubular connections. The assembly may be used with either kelly or top drive drilling systems.
These and further objects, features, and advantages of the present invention will become apparent in the following detailed description, wherein reference is made to the figures in the accompanying drawings.